Shaft roasting

Combustion/ Solid fuel-fired furnaces Fuel in direct contact Recuperative Manual and Batch, periodic Natural/self, Crucible, shaft Melting roasting Shaft, muffle... 

In the blast furnace reduction slag-making materials are also added together with a small amount of iron, the function of which is to reduce any sulphide which remains, to the product of the roasting operation to produce a sinter. The sinter is then reduced with coke in a vertical shaft blast furnace in which air is blown tluough tuyeres at the bottom of tire shaft. The temperature in the heartlr where metal is produced must be controlled to avoid the vaporization of any zinc oxide in the sinter. The products of tlris process are normally quite complex, and can be separated into four phases. Typical compositions of these are shown in Table 13.1. 

The Alexandrian seientist Hero (eirea 120 B.C.) would hardly reeognize the modern gas turbine of today as the outgrowth of his aeolipile. His deviee produeed no shaft work—it only whirled. In the eenturies that followed, the prineiple of the aeolipile surfaeed in the windmill (A.D. 900-1100) and again in the powered roasting spit (1600s). The first sueeessful gas turbine is probably less than a eentury old. 

Calcium oxide is commercially obtained from limestone. The carbonate is roasted in a shaft or rotary khn at temperatures below 1,200°C untd aU CO2 is driven off. The compound is obtained as either technical, refractory or agricultural grade product. The commercial product usually contains 90 to 95% free CaO. The impurities are mostly calcium carbonate, magnesium carbonate, magnesium oxide, iron oxide and aluminum oxide. 

S) Reduction in Water-jacket or Blast Furnaces.—At Bouc and Septemes, ores containing 30 to 40 per cent, of antimony were at first roasted in reverberatory furnaces, and the roasted product was reduced in three tuyered shaft furnaces which were worked on the spur principle with covered eye. Their dimensions were height,... 

The by-products produced in all these processes are liquation residues, matte, slags, refinery slags, and flue dust. They are added to the charges in smelting the ore, if they are sufficiently rich the liquation dross, however, is subjected to a preliminary roasting, and the flue dust is intimately mixed with lime, before smelting. Liquation residues are also sometimes treated separately in shaft furnaces. 

As well as containing iron at around 40 to 45 per cent, matte contained about 12 per cent lead, most of the copper from blast furnace feed, about half the zinc and a substantial proportion of the silver. Matte was initially roasted in open heaps or stalls to remove sulfur and was then recycled to the blast furnace, but later reverberatory roasting furnaces were used. A shaft kiln was used at the Harz smelter in Germany. 

The ore is crushed and ground and separated into various mineral concentrates by flotation. The complex lead-zinc ores have played an important role in the development of the flotation technique. A lead concentrate with perhaps 77% Pb is roasted to oxide, in general on a sinter band, a process in which sulfur is removed as sulfur dioxide. Limestone is added for slag formation and the sinter is reduced by coke in a shaft furnace. An alternative method is to use a rotating converter furnace, from which the sulfur dioxide can be used for sulfuric acid production. This is good for the environment and good for the economics of the process. 

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